1. Field of the Invention
This invention relates to the control of drug delivery apparatus, for example such apparatus for delivering a drug to a patient's lungs through inhalation.
2. Brief Discussion of Art
A number of devices are available for delivering a drug into the lungs of a patient. A pneumatic or jet-type nebulizer is particularly effective in supplying an aerosolized drug for inhalation, but other types of nebulizer are also available, such as an ultrasonic type nebulizer in which the drug to be atomized is forced through a mesh by vibrating a piezo-electric crystal, whereupon the droplets passing through the mesh are entrained in the air being inhaled by the patient. The gauge of the mesh determines the size of the droplets which enter the air stream. Alternatively, a dosimetric spacer can be used. When using a spacer, the drug is introduced into a holding chamber of the spacer, either in aerosolized form, or by loading the air within the holding chamber with the drug in powered form. The patient then breathes from the holding chamber, thereby inhaling the drug laden air. Such spacers are particularly effective when treating children or elderly patients, and for use with certain drugs. The drug is normally delivered over a number of breaths. Of course, the concentration of the drug in each breath decreases over time as a result of dilution caused by ambient air entering the holding chamber to replace the air being inhaled by the patient, and as a result of the deposition of the drug within the chamber.
In each of the above devices, a patient receives a treatment over a number of pulses or breaths. This might mean that a single treatment takes several minutes to deliver because of the amount of the drug which is to be delivered, and the nature of the device which is delivering the drug. Thus, in this specification, where a treatment is referred to, this refers to the delivery of a single dose of a drug over a number of breaths. In addition, any references to the dose refer to the quantity of a drug delivered to a patient during a treatment. In a course of treatments, a patient might be required to receive the dose of the drug twice a day, in which case the patient is required to carry out two treatments each day.
As will be appreciated from this specification, the invention applies to all different types of drug delivery device.
When a doctor prescribes a particular drug for treatment of a patient, the patient not only requires a supply of the drug, but also requires a drug delivery apparatus, for example a nebulizer or a dosimetric spacer. In the case of a nebulizer, the prescribed amount of drug for a treatment is placed in the nebulizer, and in most cases, the patient inhales from the nebulizer repeatedly until the prescribed amount of drug has been delivered. Unfortunately, this is no guarantee of the patient receiving the required dose in his or her lungs. Most of the drug tends to impact in the patient's airways before it reaches the lungs, and some of the drug is exhausted from the lungs on exhalation. Typically, about ten percent of the drug which is delivered by the atomizer reaches the lungs. However, there is a wide variation in the proportion of the drug which reaches the lungs of the patient since the effectiveness of the drug delivery depends on the way in which the patient uses the device. If the patient inhales deeply and regularly, then plenty of the drug will reach the lungs. However, for patients exhibiting symptoms of pulmonary disease, breaths will be shallower and treatment may be interrupted by symptoms of their disease such as coughing. This will substantially reduce the amount of the drug delivered to the patient such that they will not receive as much of the drug as their doctor intends.
More recently, the applicant for this patent has put on the market a nebulizer which calculates the dose of the drug which the patient receives in his lungs. The nebulizer is supplied to the patient pre-programmed with the dose of a particular drug which the patient requires. The patient is prescribed a particular drug, and before use the patient will insert the drug, usually in liquid form, into the nebulizer. The patient then starts inhaling from the nebulizer and the drug is delivered to the patient. The atomizer is arranged such that it only delivers the drug during the first fifty percent of the inhalation phase of the patient, and the flow rate of inhalation of the patient through the device is measured, and from this, the dose of drug received by the patient can be calculated. Once the pre-programmed dose has been delivered, the nebulizer will automatically stop atomizing the drug regardless of whether or not any drug remains within the nebulizer which has not been atomized. The atomizer must be reset before the next dose of the drug is delivered. This device is disclosed in Medic-Aid Limited's earlier patent publication (GB-A-2316323), and we hereby incorporate the information contained therein by this reference in its entirety.
Whilst the applicant's product has significantly improved the accuracy of drug delivery, if the patient's doctor wishes to change the dose of the drug delivered to the patient, or to change the prescribed drug altogether, it is necessary to return the nebulizer for reprogramming, or to replace it with one with the correct drug and dose details. In a known drug delivery system, the prescribed drug for each treatment is supplied in separate drug vials, each of which contains the required drug for a single treatment. Thus, a number of vials will normally be supplied to the patient for use one at a time over a period of, typically, one month. In that arrangement, each drug vial carries a bar code thereon such that, before each treatment, the bar code is read by a bar code reader on the atomizer to identify what the drug is which is to be delivered. However, the bar code must be attached to each vial, requiring increased manufacturing costs and also the carrying out of regulatory approval tests to ensure that the adhesives of the label and the dyes used will not contaminate the drug within the plastic vials or reduce the storage life of the product. Long term stability testing over two or three years is required.
According to another prior art arrangement, narcotic drugs are delivered using an atomizer for pain relief In that case, it is clearly important to restrict access to the use of the drug delivery apparatus with that drug to the patient concerned. The patient is supplied with an I-button which is kept separate from the drug and the atomizer, and which must be touched against a contact surface on an atomizer in order to activate it for a treatment. The button is merely used as a key to unlock the atomizer for a single treatment.